In conventional wireless networks, fixed numerologies have been employed to allow for an ease of design. The parameters of the numerology are typically set based on an understanding of the normal usage parameters of the network. In future networks, a more diverse set of needs should be served. Future networks may operate at a variety of different frequencies and serve a variety of different devices. Satisfying the diverse requirements for future wireless networks, such as fifth generation (5G) wireless networks, may be accomplished according to multiple approaches. In a first approach, which may be considered backward compatible with LTE, sampling frequencies and subcarrier frequencies are selected as integer multiples of the sampling frequencies and subcarrier frequencies already established for LTE. In a second approach, which may be considered to have so-called forward compatibility, the sampling frequencies and subcarrier frequencies are closely related to the sampling frequencies and subcarrier frequencies set for LTE, but are non-integer multiples. For the first approach, the backward compatible to LTE solution, there are two versions of the solutions based on the number of symbols and cyclic prefix (CP) lengths in a sub-frame or transmission time interval. First version solutions are strictly compatible with LTE and involve using seven symbols or “7(1,6)” symbols in a sub-frame. The notation 7(1,6) represents a scheme with a first CP length for one symbol among the seven symbols and a second CP length for the other six symbols. For strict compatibility with LTE, the two CP lengths and the CP overhead in the base subcarrier spacing of 15 kHz are arranged to be the same as the two CP lengths and the CP overhead of current LTE. The second version solutions may be seen as closely compatible to LTE in the sense that their CP overhead and seven symbols in a sub-frame are the same as the CP overhead and the number of symbols used for current LTE, however, the symbols with different CP lengths are distributed in a manner distinct from LTE, e.g., 7(3,4) and 7(2,5).
In LTE, the parameter transmission time interval (TTI) is used to refer to the transmission time for a defined set of OFDM symbols. In some examples, TTI can also be referred to as a “transmission time unit (TTU)” or “sub-frame duration”, which indicates the physical (PHY) layer symbol and frame time structure. Similar to TTI, TTU and “sub-frame duration” are each equal to the sum of the useful symbol duration and any symbol overhead such as cyclic prefix CP time for all of the OFDM symbols include in a set. For the second approach, with so-called forward compatibility, a flexible number of symbol configurations may be considered per transmission time interval (TTI). For any base SS, any number of symbols per TTI can be configured. This may be referred to as a discretionary N (dN) solution, based on the diverse requirements of applications, such as latency, control/data, TDD/FDD configurations, and co-existence, etc. As will be addressed hereinafter, the term “co-existence” relates to two or more sub-bands in use for a given connection employing compatible numerologies.
In LTE, a channel bandwidth and a transmission bandwidth are defined, where the channel bandwidth is defined as the bandwidth of a carrier while the transmission bandwidth is defined as the number of available RB (Resource Block) in the carrier. In LTE, since RBs with different subcarrier spacing occupy same bandwidth, the transmission bandwidth can apply to all subcarrier spacing.
However, in New Radio (NR), 12, the number of subcarriers, is same for all RBs with different subcarrier spacing. Hence subcarrier spacing sets suitable for different channel bandwidth are different. Then it should be determined for the relationships among channel bandwidth, transmission bandwidth and subcarrier spacing.
In LTE, the channel bandwidth includes a useful transmission bandwidth and guide band, where the guide band is about 10% of the channel bandwidth for sub-6 GHz bands. In NR, the higher spectrum efficiency can be achieved, where that the guide band can be reduced significantly or even can be removed, for example, 1% of the channel bandwidth can be used for guide band.
To determine a channel bandwidth for a given subcarrier spacing, the number of the subcarriers used in the channel bandwidth should be constrained by the reasonable implementation costs, for example, FFT size or sampling rate. As a result, the maximum channel bandwidth for the given subcarrier spacing, and the available maximum channel bandwidths are different for different subcarrier spacing options.